Despite the terminology self-radicalisation is often a shared endeavour with other like-minded extremists over the internet.
In that sense, no “lone actor” is really alone, they are surrounded by multiple sources of motivation to do what they do.
Police are not currently looking for anyone else in connection with the killing of British MP David Amess, but whether the assailant was truly acting “alone” is still unclear. Ali Harbi Ali has been remanded in custody and can be questioned until Friday.
The security services have never liked the concept of the "lone wolf". They believe it glamorises the attacker, and they prefer to call them “lone actors”.
A senior counter-terrorism official, speaking recently, said his concerns were about what the professionals prefer to view as “self-initiated terrorists”.
They will search for clues in the electronic devices of Ali Harbi Ali, 25, from Tufnell Park, North London – his laptop, tablet, mobile phone, memory sticks and electronic communications – and in his travel patterns.
Among the questions to resolve is what led to the choice of victim: Sir David, a Conservative Party stalwart but not a minister, and with no close connection to the government.
Amess was the second MP to be killed in little over five years. In the last incident in June 2016, a week before the Brexit vote to leave the EU, the victim was the Labour MP Jo Cox.
Thomas Mair, her murderer, was heard to say “this is for Britain” during the attack and he was radicalised by extremist material. In a raid of his home nearby, police found Nazi-related material. A Google search was found on his computer logs for the deadly impact of a round from a .22 rifle.
Sources say Ali was referred to the government's Prevent programme as a teenager in an effort to divert him from extremism but that his involvement was “short”.
Many referrals come from schools, which are under a legal obligation to report extremist behaviour.
Sometimes the subject of the referral, or their parents, convince a panel that they do not need “intervention” work with a mentor, and the case is parked for review later.
Whatever the concern, it was not sufficient to make it on to a list of MI5 casework of individuals suspected of attack planning and their associates, security sources said.
Security sources have also been worrying for some months that lockdown may have exacerbated the problem of online “self-radicalisation”.
Mr Ali's involvement appears to be more longstanding, but lockdown may have prompted an increased sense of “exclusion and isolation”, a risk highlighted by security sources in recent times.
The ability of groups to recruit, train and direct terrorists from their own soil has been gradually eroded since the training camps established in Afghanistan before 9/11.
But they have been increasingly successful in pumping out inspirational and instructional material of an ever-higher quality.
Sir David Amess incident - in pictures
Where Al Qaeda leaders delivered lectures with a Kalashnikov propped by their side, recorded on fuzzy videos tapes, the modern terrorist production is more like a Hollywood film.
Inspiration is drawn from such films which titles such as Flames of War and Flames of War 2, that feature executions and torture, or give detailed explanations of how to choose a knife and conduct an attack.
Commander Richard Smith, who leads Scotland Yard's Counter-Terrorism Command, spoke in June about the harmful nature of online extremism.
"That is why it is important that anyone who believes that they have a friend or loved one who they think has been radicalised, or is vulnerable, seeks help," he added.
In this case, the suspect's heritage in Somalia may have involved trips there and may have involved meeting radicals connected to Al Shabab, the militant group aligned with ISIS.
They recruited about 50 British members, some of whom rose to be senior members, like Bilal Al Berjawi, from Lisson Grove, West London, who was killed in a drone strike in 2012. Both Michael Adebolajo, one of the killers of Fusilier Lee Rigby and Mohammed Emwazi, the ISIS executioner, tried to join the group.
The alleged killer remained at the scene of the crime, where he was arrested and perhaps suggesting that he was suicidal.
He would have been justified in suspecting that armed police would arrive and shoot him dead, since that was what happened with incidents in Streatham, south London, in February 2020, and at Fishmongers’ Hall, central London, in November 2021, and at Borough Market in June 2017.
The difference in those cases was that the suspects had fashioned fake suicide vests to ensure their imagined journey to paradise.
In this instance, there could have been a desire to deliver a message, in the way that Michael Adebolajo did after stabbing to death Fusilier Lee Rigby outside Woolwich Barracks in May 2013.
That message has not been delivered but something has led the police to declare the case, late on Friday night, as a terrorist investigation – an attack motivated by a political, religious or ideological cause.
His father is said to be “traumatised” by what his son's arrest. Harbi Ali Kullane, 60, a former director of communications for the Somali prime minister, moved to Britain in the 1990s and married Mr Ali’s mother, Jamila, in Southwark, south London, in 1999.
The children were all born in Britain – Ali the eldest; two sisters, now in their early twenties; and a younger brother, aged 16; all brought up in Croydon, south London.
Their parents split up and Mr Kullane moved to north London, having returned to Somalia in the 2010s to work for the government there. The father appears to have siblings who work as a healthcare professor in Sweden and as a Somali diplomat in China.
Ali himself appears to have been living with an aunt and cousins in another part of north London. He was reportedly training to work in healthcare.
Whatever the motivations, the drive to commit such acts can be very mixed up.
In the case of Salman Abedi, the Manchester Arena bomber, he had travelled back and forth between Britain and Libya but the inspiration appears to have come from Syria.
Abedi was not uncommon in mixing personal failings with religious overtones and grievances drawn from international conflicts in many arenas.
Investigators are dealing with a complex mix of heritage, extremist ideology, online and offline grooming as well as the stresses of the pandemic and daily life. Their challenge is tying those factors together into an explanation for why Amess was killed and how to stop it happening again.
